The present invention relates generally to the field of integrated circuits and to methods of manufacturing integrated circuits. More particularly, the present invention relates to a method of forming integrated circuit features via a titanium hard mask.
Semiconductor devices or integrated circuits (ICs) can include millions of devices, such as, transistors. Ultra-large scale integrated (ULSI) circuits can include complementary metal oxide semiconductor (CMOS) field effect transistors (FET). Despite the ability of conventional systems and processes to put millions of devices on an IC, there is still a need to decrease the size of IC device features, and, thus, increase the number of devices on an IC.
One limitation to the smallness of IC critical dimensions is conventional lithography. In general, projection lithography refers to processes for pattern transfer between various media. According to conventional projection lithography, a silicon slice, the wafer, is coated uniformly with a radiation-sensitive film or coating, the photoresist. An exposing source of radiation (such as light, x-rays, or an electron beam) illuminates selected areas of the surface through an intervening master template, the mask, for a particular pattern. The lithographic coating is generally a radiation-sensitized coating suitable for receiving a projected image of the subject pattern. Once the image is projected, it is indelibly formed in the coating. The projected image may be either a negative or a positive image of the subject pattern.
Exposure of the coating through a photomask or reticle causes the image area to become selectively crosslinked and consequently either more or less soluble (depending on the coating) in a particular solvent developer. The more soluble (i.e., uncrosslinked) or deprotected areas are removed in the developing process to leave the pattern image in the coating as less soluble polymer.
Projection lithography is a powerful and essential tool for microelectronics processing. As feature sizes are driven smaller and smaller, optical systems are approaching their limits caused by the wavelengths of the optical radiation.
One alternative to projection lithography is EUV lithography. EUV lithography reduces feature size of circuit elements by lithographically imaging them with radiation of a shorter wavelength. xe2x80x9cLongxe2x80x9d or xe2x80x9csoftxe2x80x9d x-rays (a.k.a, extreme ultraviolet (EUV)), wavelength range of lambda=50 to 700 angstroms are used in an effort to achieve smaller desired feature sizes (134 in particular).
In EUV lithography, EUV radiation can be projected onto a resonant-reflective reticle. The resonant-reflective reticle reflects a substantial portion of the EUV radiation which carries an IC pattern formed on the reticle to an all resonant-reflective imaging system (e.g., series of high precision mirrors). A demagnified image of the reticle pattern is projected onto a resist coated wafer. The entire reticle pattern is exposed onto the wafer by synchronously scanning the mask and the wafer (i.e., a step-and-scan exposure).
Although EUV lithography provides substantial advantages with respect to achieving high resolution patterning, errors may still result from the EUV lithography process. For instance, the reflective reticle employed in the EUV lithographic process is not completely reflective and consequently will absorb some of the EUV radiation. The absorbed EUV radiation results in heating of the reticle. As the reticle increases in temperature, mechanical distortion of the reticle may result due to thermal expansion of the reticle.
Both conventional projection and EUV lithographic processes are limited in their ability to print small features, such as, contacts, trenches, polysilicon lines or gate structures. As such, the critical dimensions of IC device features, and, thus, IC devices, are limited in how small they can be.
Thus, there is a need to pattern IC devices using non-conventional lithographic techniques. Further, there is a need to form smaller feature sizes, such as, smaller contact holes and trench lines. Yet further, there is a need to form integrated circuit features by oxidation of titanium hard mask.
An exemplary embodiment is related to a method of forming integrated circuit device features by oxidization of a titanium hard mask. This method can include providing a photoresist pattern of photoresist features over a first layer of material deposited over a second layer of material; etching the first layer of material according to the photoresist pattern to form material features; oxidizing exposed portions of the material features where the material features are made of a material which expands during oxidation; and etching the second layer of material according to the material features which have expanded as a result of oxidation. Advantageously, the expansion of the material features results in a smaller distance between material features than the distance between photoresist features.
Briefly, another exemplary embodiment is related to a method of manufacturing an integrated circuit. This method can include depositing a photoresist material over a layer of titanium deposited over an inter-level dielectric (ILD) layer; etching the photoresist material to form photoresist features having a first separation distance from each other; etching the layer of titanium using the photoresist features as a mask to form titanium features; and oxidizing the titanium features such that the titanium features expand and are separated from each other by a second separation distance. Advantageously, the second separation distance is less than the first separation distance.
Briefly, another embodiment is related to an integrated circuit having trench lines. This integrated circuit is manufactured by a method which can include providing a photoresist pattern of photoresist features over a first layer of material deposited over a second layer of material; etching the first layer of material according to the photoresist pattern to form material features; oxidizing exposed portions of the material features where the material features are made of a material which expands during oxidation; and etching the second layer of material according to the material features which have expanded as a result of oxidation. Advantageously, the expansion of the material features results in a smaller distance between material features than the distance between photoresist features.
Other principle features and advantages of the present invention will become apparent to those skilled in the art upon review of the following drawings, the detailed description, and the appended claims.